The present invention relates to a power train output which is used to take out the power from an automatic transmission of a tractor or the like to an attached apparatus or other apparatus and, more particularly, to a brake unit to stop the rotation of the output shaft of the power train output upon the supply of a brake hydraulic operating pressure.
Hitherto, in automatic transmissions of a tractor or the like, a power train output which is directly coupled to a power output shaft from the engine and which serves to take out the power to an attached apparatus or other apparatus is provided, and a brake unit to stop the rotation of the output shaft due to the hydraulic pressure is built into the power train output.
Such a brake unit has a structure such that brake plates are alternately arranged between the spline hub of a brake drum fixed to the output shaft and the spline hub on the fixed side, and the rotation side and the fixed side of the brake plates are brought into contact by means of the pressure of the brake piston due to the supply of the hydraulic pressure and thereby causing braking.
On the other hand, the brake piston which is made operative by way of the hydraulic pressure is ordinarily mechanically returned by use of a return spring. Practically speaking, the return spring is assembled between the brake piston and a fixed part of the housing or the like. The return spring is compressed due to the movement of the brake piston due to the hydraulic pressure. Then, upon release of the hydraulic pressure, the brake piston is pushed and returned to the brake release position by means of the force of the return spring.
However, in such a conventional return structure of the brake piston, the space needed to accommodate the return spring has to be provided between the brake piston and the housing serving as the fixed side. Thus, there are problems such that the structure of the brake unit becomes complicated and also the brake unit is increased in size to provide enough space for the return spring.